Method of generation of spontaneous elastic-spin-oscillations in ferromagnetopiezosemiconductor circuits

ABSTRACT

A method of generating spontaneous elastic-spin-oscillations in ferromagneto-piezosemiconductor circuits, including a slab of ferromagnetic crystal and a semiconductor layer on said slab, comprises applying a d.c. voltage through ohmic contacts to the semiconductor layer to produce surface and transverse oscillations the surface oscillations inducing in a semiconductor layer, a current of drifting electrons, modulating the current of drifting electrons by a piezoelectric field induced by elastic oscillations in the layer caused by the elastic spin oscillations in the ferromagnetic crystal, amplifying the elastic oscillations in the piezosemiconductor layer by the current when the drifting electrons are at a critical drift of velocity, amplifying the elastic oscillations in the ferromagnetic crystal when the elastic oscillations in the piezosemiconductor are amplified, the circuit being in a state of spin-acoustic resonance by placing the circuit in a constant magnetic field having a value determined by the circuit parameters, and producing a multiplication of spin oscillations through elastic-spin couplings, wherein the dimensions of the slab ensure a maximum reflection from the boundary borders of the slab when the surface oscillations meet Sommerfeld boundary conditions and when the transverse oscillations ensure a maximum reflection from the surface vertical to the direction of the propagation of elasticspin waves.

United States Patent Kaliski [54] METHOD OF GENERATION OF SPONTANEOUS ELASTIC-SPIN- OSCILLATIONS IN FERROMAG NETOPIEZOSEMICONDUCTOR CIRCUITS [72] Inventor: Sylwester Kaliski, ul. Einsteina, Warszawa 49, Poland [22] Filed: Dec. 14, 1970 [21] Appl. No.: 97,499

[30] Foreign Application Priority Data Dec. 13, 1969 Poland ..137535 52 0.8. CI 051$: ..3l0/8.l, 310/82, 310/95, 310/97, 333/30 R 51 rm. Cl. ..H0lv 7 00 [5 8] Field of Search.

Stern, Microsound Components, Circuits, and Applica- [4 1 June 6,1972

tions, Ultrasonics, October, 1969, 227- 233.

Primary Examiner-William M. Shoop, Jr. Assistant Examiner-B. A. Reynolds Attorney-Waters, Roditi, Schwartz & Nissen [5 7] ABSTRACT A method of generating spontaneous elastic-spin-oscillations in ferromagneto-piezosemiconductor circuits, including a slab of ferromagnetic crystal and a semiconductor layer on said slab, comprises applying a dc. voltage through ohmic contacts to the semiconductor layer to produce surface and transverse oscillations the surface oscillations inducing in a semiconductor layer, a current of drifting electrons, modulating the current of drifting electrons by a piezoelectric field induced by elastic oscillations in the layer caused by the elastic spin oscillations in the ferromagnetic crystal, amplifying the elastic oscillations in the piezosemiconductor layer by the current when the drifting electrons are at a critical drift of velocity, amplifying the elastic oscillations in the ferromagnetic crystal when the elastic oscillations in the piezosemiconductor are amplified, the circuit being in a state of spin-acoustic resonance by placing the circuit in a constant magnetic field having a value determined by the circuit parameters, and producing a multiplication of spin oscillations through elasticspin couplings, wherein the dimensions of the slab ensure a maximum reflection from the boundary borders of the slab when the surface oscillations meet Sommerfeld boundary conditions and when the transverse oscillations ensure a maximum reflection from the surface vertical to the direction of the propagation of elastic-spin waves.

5 Claims, 2 Drawing Figures MEANS FOR PRODUCING CONSTANT MAGNETIC FIELD PATENTEDJUR 61912 3568.441

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MEANS FOR PRODUCING CONSTANT MAGNETIC FIELD METHOD OF GENERATION OF SPONTANEOUS ELASTIC-SPIN-OSCILLATIONS IN FERROMAGNETOPIEZOSEMICONDUCTOR CIRCUITS BACKGROUND OF THE INVENTION The invention relates to a method of generation of spontaneous elastic-spin-oscillations in ferro-magnetopiezosemiconductor circuits.

A prior art method of generation of spontaneous elastic oscillations in a piezosemiconductor crystal, to which dc. voltage is applied, involves therein a current of drifting electrons which, at a critical velocity, amplifies the spontaneous oscillations in the crystal with frequencies equalling the natural frequencies of the crystal.

This method, however, is limited to lateral and longitudinal oscillations.

There is another prior art method of obtaining spontaneous surface oscillations of elastic waves in a slab of a piezosemiconductor crystal, in which,'through irradiation, a thin subsurface semiconducting layer is formed. In the surface under the influence of an applied dc. voltage, a current of drifting electrons is generated, which at a critical drift velocity amplifies the spontaneous oscillations of elastic surface waves that exist in the crystal, in which the maximum reflection of the waves from the slab border is achieved due to fulfillment of Sommerfeld boundary conditions. Sommerfeld boundary conditions are known in the field of physics as conditions determining the dependence of the dimensions of a crystal upon the frequency of the wave, and thus upon the wavelength.

The compliance with Sommerfeld boundary conditions in the case of propagation of a surfacial wave consists in that the normal stresses and the tangential displacements in the crystal on its boundary surface are simultaneously equal to zero, or inversely, i.e., the tangential stresses and normal displacements on the boundary surface of the crystal are equal to zero.

In order to ensure a complete reflection of the wave from the boundary surface, the length of the crystal is assumed to be a multiple of the half-wave propagating in the crystal. In order to eliminate the possibility of boundary disturbances from the side surface of the crystal, the width of the crystal is preferably assumed as being equal to from several to wavelengths. The thickness of the crystal, ensuring a propagation not disturbed by itself, must be greater than the wavelength, as the surfacial wave declines at the depth of a magnitude order of the wavelength.

SUMMARY OF THE INVENTION An object of the invention is to produce multiplied elasticspin-oscillations with frequencies having a range of hundreds to thousands MI-Iz due to the utilization of the effect of critical velocity of electron drift and the inner mechanism of elasticspin coupling in ferromagnetic crystals.

The above and additional objects are achieved due to the application of a circuit having at the same time ferromagnetic and piezosemiconductor properties.

The invention provides in a ferromagneto-semiconductor circuit comprising a ferromagnetic crystal and a layer of piezosemiconductor layer, that dc. voltage be applied through ohmic contacts to the semiconductor layer, which generates a current of electrons drifting in the layer.

In the ferromagnetic crystal in which the full reflection of surface waves from the crystal border is obtained, due to the fulfillment of the Sommerfeld boundary conditions, the selfexcited elastic-spin surface oscillations generate in the semiconductor layer through the mechanical contact between the crystal and the layer, elastic waves which involve therein a piezoelectric field. At a critical drift velocity of electrons, due to the piezoelectric effect, there arise an amplification of the elastic oscillations in the layer which, subsequently, multiply the elastic-spin oscillation in the crystal.

The elastic-spin coupling that produces spin oscillations is the highest in conditions of spin-acoustic resonance, which is achieved by placing the crystal in a constant magnetic field having a value determined by the parameters of the circuit.

In order to obtain spontaneous elastic-spin transverse oscillations, a ferromagneto-semiconductor monolithic crystal is employed in which the electron mobility has a value which enables the critical velocity to be achieved. Since crystals of such type with sufficient mobility are not available, the circuit can be implemented by a superposition one upon another of ferromagnetic and semiconductor crystal layers with a slab thickness smaller than the required wave length. The principle of operation of the circuit is analogous to the circuit for the surface oscillations.

BRIEF DESCRIPTION OF THE DRAWING:

FIG. 1 shows an example of an embodiment of the circuit comprising a slab of iron-yttrium garnet and a sub-surface semiconductor layer of cadmium sulfide for achieving spontaneous surface oscillations, and

FIG. 2 shows an example of an embodiment of the circuit consisting of alternately superposed layers of iron-yttrium garnet and cadium sulfide for obtaining transverse oscillations.

DETAILED DESCRIPTION The elastic-spin surface oscillations arising under the influence of thermal fluctuations in a slab l of FIG. I generate in a semiconducting layer 2 elastic oscillations which generate a piezoelectric field that modulates the current of drifting electrons in the layer 2, generated by dc. voltage from source 4 applied to this layer through ohmic contacts 3. Slab 1, illustratively is iron-yttrium garnet while layer 2 is, illustratively cadmium sulfide.

At a critical drift velocity through the piezoelectric effect, an amplification of elastic oscillations in the layer 2 takes place which, in turn, amplifies the elastic oscillations in the slab 1. To obtain transverse elastic-spin oscillations, FIG. 2 shows the dc. voltage from source 4 applied through ohmic contacts 3 to the lateral surfaces of a multi-layer circuit. When this circuit is located within the spin-acoustic resonance condition, which is achieved by placing the circuit in the constant magnetic field, as determined by the parameters of the circuit, a multiplication of spin oscillations results.

The oscillations at the required frequency can be obtained by securing the full reflection from the boundary borders by fulfilling the Sommerfeld boundary conditions in case of surface oscillations, and in the case of transverse oscillations by securing the full reflection from the surfaces vertical to the direction of the propagation of elastic-spin waves.

The semiconductor layer can be superposed upon the slab either mechanically or epitaxially. I

To obtain surface oscillations a natural cooling of the circuit will sufiice, but for the transverse oscillation an additional cooling can be applied, which will ensure a continuous operation of the circuit.

What is claimed is:

l. A method of generation of spontaneous elastic-spin oscillations in ferromagneto-piezosemiconductor circuits comprising a slab of a ferromagnetic crystal and a semiconductor layer on said slab, which method comprises applying a dc voltage through ohmic contacts to the semiconductor layer to produce surface oscillations, said surface oscillations inducing in the semiconductor layer a current of drifting electrons, modulating said current of drifting electrons by a piezoelectric field induced by elastic oscillations in the layer caused by the surface oscillations in said ferromagnetic crystal, amplifying the elastic oscillations in the semiconductor layer by said current when said drifting electrons are at a critical drift velocity, amplifying the elastic oscillations in the ferromagnetic crystal when said elastic oscillations in said semiconductor are amplified, said circuit being in the state of spin-acoustic resonance by placing the circuit in a constant magnetic field having a value determined by the circuit parameters, and producing a multiplication of spin oscillations through elastiction.

3. A method according to claim 1, wherein said slab is ironyttrium garnet and said semiconductor layer is cadmium sul- 4. A method according to claim 2, wherein said semiconductor layer is superposed on said slab epitaxially.

5. A method according to claim 2, wherein said semiconductor layer is superposed on said slab mechanically. 

2. A method according to claim 1, including producing transverse oscillation in the circuit with alternately superposed layers of ferromagnetic and semiconductor crystals, said d.c. voltage being applied to the lateral surfaces of the circuit having dimensions ensuring a maximum reflection of wave from the surfaces vertical to the direction of its propagation.
 3. A method according to claim 1, wherein said slab is iron-yttrium garnet and said semiconductor layer is cadmium sulfide.
 4. A method according to claim 2, wherein said semiconductor layer is superposed on said slab epitaxially.
 5. A method according to claim 2, wherein said semiconductor layer is superposed on said slab mechanically. 